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Petri Nets for Modelling and Analysing Trophic Networks

Baldan P., Bocci M., Brigolin D., Cocco N., Heiner M., Simeoni M.

Fundamenta Informaticae

2018

Vol. 160, nr 1/2

27--52

We consider trophic networks, a kind of networks used in ecology to represent feeding interactions (what-eats-what) in an ecosystem. Starting from the observation that trophic networks can be naturally modelled as Petri nets, we explore the possibility of using Petri nets for the analysis and simulation of trophic networks. We define and discuss different continuous Petri net models, whose level of accuracy depends on the information available for the modelled trophic network. The simplest Petri net model we construct just relies on the topology of the network. We also propose a technique for deriving a more refined model that embeds into the Petri net the known constraints on the transition rates that represent the knowledge on metabolism and diet of the species in the network. Finally, if the information of the biomass amounts for each species at steady state is available, we discuss a way of further refining the Petri net model in order to represent dynamic behaviour. We apply our Petri net technology to a case study of the Venice lagoon and analyse the results.

A Causal View on Non-Interference

Baldan P., Carraro A.

Fundamenta Informaticae

2015

Vol. 140, nr 1

1--38

The concept of non-interference has been introduced to characterise the absence of undesired information flows in a computing system. Although it is often explained referring to an informal notion of causality - the activity involving the part of the system with higher level of confidentiality should not cause any observable effect at lower levels - it is almost invariably formalised in terms of interleaving semantics. Here we focus on Petri nets and on the BNDC (Bisimilarity-based Non-Deducibility on Composition) property, a formalisation of non-interference widely studied in the literature. We show that BNDC admits natural characterisations based on the unfolding semantics - a classical true concurrent semantics for Petri nets - in terms of causalities and conflicts between high and low level activities. This leads to algorithms for checking BNDC on various classes of Petri nets, based on the construction of suitable complete prefixes of the unfolding. We also developed a prototype tool UBIC (Unfolding-Based Interference Checker), working on safe Petri nets, which provides promising results in terms of efficiency.